Ping request timeout bug

Similar to a previous thread, there is a definate bug with the ping tool or at least the DLLs it's using.
On Vista and Windows 7 if the timeout is lower than 500ms there are random timeouts shown. The number of timeouts is related to the actual round trip delay, very few if the RTT is low (<5ms) rising as the RTT gets higher ( I get about 2% loss showing at 12ms RTT).
I checked the output with Wireshark.
Pings are sent and recieved for a while then at some point the PC will send an ICMP destination unreachable in response to an ICMP reply. So the ping gets a reply but the reply is ignored for some reason and an ICMP destination unreachable sent. I've checked the identification tag so can confirm the unreachable message is in response to the ICMP repy.
I have tested the same behavior with another ping tool called pingtester and seen the same bug so it will be related to a common component between the two programs, maybe in Windows itself?.
I don't see the bug using Windows 2003 Server.